Forward acoustic scattering based double-transmitter and double-receiver networking target detection system and method thereof

ABSTRACT

The present invention relates to a forward acoustic scattering based double-transmitter and double-receiver networking target detection system and method thereof. Two transmitting ends and two receiving ends are adopted, anchored at a sea bottom, and arranged in a parallelogram layout. Time of a target crossing transmitting-receiving connection lines is extracted by adopting a proper direct wave suppression method; and unknown parameters of the horizontal distance, the target velocity and the included angle between the target track and the transmitting-receiving connection lines are estimated at corresponding moving time intervals when the target crosses the four transmitting-receiving connection lines according to different crossing modes. An arrangement mode is simple and flexible, and monitoring of sea areas and sea channels can be realized. The information of the time of the target crossing the transmitting-receiving connection lines, extracted by the method, is more accurate and reliable.

FIELD OF THE INVENTION

The present invention belongs to range measurement methods of underwatertargets, and relates to a forward acoustic scattering baseddouble-transmitter and double-receiver networking target detectionsystem and method thereof. The present invention can be used fordetecting underwater moving targets that intrude into double-basetransmitting-receiving connection lines, can realize range measurement,direction measurement and velocity measurement of the targets, and canbe applicable to double-transmitter double-receiver andmulti-transmitter multi-receiver detection cases, wherein a transmittingend may refer to a single transducer or a transmitting array; and areceiving end may refer to a single hydrophone or a receiving array. Thepresent invention belongs to the fields of underwater sound engineering,ocean engineering, sonar technologies, etc.

BACKGROUND OF THE INVENTION

Forward acoustic scattering is mainly used for detecting underwaterinvading targets which are close to transmitting-receiving connectionlines or which cross the transmitting-receiving connection lines. Inthis case, since forward scattering intensity of the targets is greaterthan intensity in a reverse direction and other directions, a forwardscattering wave and a direct wave which arrive at receiving endsinterfere with each other and enable a receiving sound field tofluctuate. After direct wave suppression, distortion of the forwardscattering wave or the receiving sound field can be extracted.

When the position of the target is close to the transmitting-receivingconnection lines, the range resolution of the detection system for thetarget is infinite. Even if a forward scattering signal of the targetcan be extracted through a direct wave suppression method, distanceinformation of the invading target cannot be extracted from the forwardscattering signal. Therefore, in a forward acoustic scattering basedtarget detection system under a single-transmitter single-receiverconfiguration, range measurement cannot be performed for the target andvelocity and course information of the target cannot be known.

In published literature data, the distance information of the targetthat invades into the transmitting-receiving connection lines isextracted in a single-transmitter double-receiver configuration mode. Inthis configuration condition, two transmitting-receiving connectionlines exist. It is assumed that a length of the transmitting-receivingconnection lines is l, a spacing of two hydrophones is h and h isgreatly less than l. A horizontal distance from a crossing point of thetarget on the transmitting-receiving connection line to the transmittingend is marked as d, and it is assumed that the moving velocity v of thetarget is a known quantity. Time of the target crossing twotransmitting-receiving connection lines are measured as t₁ and t₂, andthen a course of the target between the two transmitting-receivingconnection lines can be indicated as v(t₂−t₁). According to a trianglesimilarity relationship, d=v(t₂−t₁) l/h can be directly obtained.Crossing time t₁ and t₂ can be extracted through an extraction method ofsound field distortion, and substituted into a formula to obtainestimated values about the target distance.

However, in practical application, the method has two obviousdefects: 1. the moving velocity information of the target in practicalapplication belongs to an unknown quantity and cannot be known inadvance. 2. The method for extracting the crossing time of the target bydirectly observing sound field fluctuation is not reliable. Therefore,in practical application, the method for extracting the distanceinformation of the moving target that crosses the transmitting-receivingconnection lines in a single-transmitter multi-receiver mode isinfeasible.

SUMMARY OF THE INVENTION

The present invention proposes a forward acoustic scattering baseddouble-transmitter double-receiver networking target detection systemand method thereof to avoid defects of the prior art, which can beapplicable to double-transmitter double-receiver and multi-transmittermulti-receiver detection cases. The present invention can be used fordetecting underwater moving targets that intrude intotransmitting-receiving connection lines, and can realize rangemeasurement, direction measurement and velocity measurement of thetargets.

A forward acoustic scattering based double-transmitter double-receivernetworking type target detection system comprises two transmitting endsand two receiving ends, wherein the two transmitting ends and the tworeceiving ends are anchored at a sea bottom, and formed in aparallelogram layout; the two transmitting ends are respectively markedas T_(x1) and T_(x2); the two receiving ends are respectively marked asR_(x1) and R_(x2); T_(x1)-R_(x1), R_(x1)-R_(x2), R_(x2)-T_(x2) andT_(x2)-T_(x1) form four edges of the parallelogram; T_(x1)-R_(x2) andT_(x2)-R_(x1) are two diagonal lines of the parallelogram; a length ofT_(x1)-R_(x1) is marked as l; a length of R_(x1)-R_(x2) is marked as h;an included angle between T_(x1)-T_(x2) and T_(x2)-R_(x2) is marked asα; and four transmitting-receiving connection lines are formed:T_(x1)-R_(x1), T_(x1)-R_(x2), T_(x2)-R_(x1) and T_(x2)-R_(x2); anddepths of the transmitting ends and the receiving ends are equal.

The number of transmitting sound sources of the transmitting ends is ina range of 2-50; the number of receiving hydrophone arrays is in a rangeof 2-50; and a multi-transmitter multi-receiver forward detection systemis formed.

A spacing of the transmitting sound sources is 10-10000 meters.

A spacing of the receiving hydrophone arrays is 10-10000 meters.

A method for detection by using the forward acoustic scattering baseddouble-transmitter and double-receiver networking target detectionsystem comprises the following steps of estimating unknown parameters ofd, v and γ when a target successively crosses T_(x1)-R_(x1),T_(x2)-R_(x1), T_(x1)-R_(x2) and T_(x2)-R_(x2) at uniform velocity valong a straight line, with a horizontal distance from a crossing pointof the target on the transmitting-receiving connection lineT_(x1)-R_(x1) to R_(x1) marked as d and an included angle between atarget track and the transmitting-receiving connection lineT_(x1)-R_(x1) marked as γ:

step 1: extracting time of the target crossing transmitting-receivingconnection lines by adopting a direct wave suppression method, whereinsince four transmitting-receiving connection lines exist under adouble-transmitter double-receiver configuration, four time aresuccessively marked as t₁, t₂, t₃ and t₄ according to a time sequence;

step 2: calculating corresponding moving time intervals when the targetcrosses the four transmitting-receiving connection lines as Δt₂₁=t₂−t₁,Δt₃₂=t₃-t₂ and Δt₄₃=t₄−t₃;

step 3: substituting parameters of Δt₂₁, Δt₃₂, Δt₄₃ and l into thefollowing formula to obtain an estimated value of a target distance d:

$d = {\frac{\Delta\;{t_{21}\left( {{\Delta\; t_{21}} + {\Delta\; t_{32}} - {\Delta\; t_{43}}} \right)}}{\Delta\;{t_{32}\left( {{\Delta\; t_{21}} + {\Delta\; t_{32}} + {\Delta\; t_{43}}} \right)}}l}$

wherein l is a length of T_(x1)-R_(x1);

step 4: substituting parameters of Δt₂₁, Δt₃₂, Δt₄₃, l, h and α into thefollowing formula to obtain an estimated value of an inclined angle α ofa target track:

$\gamma = {\tan^{- 1}\left( \frac{1}{{\frac{l}{h\;\sin\;\alpha}\frac{{\Delta\; t_{21}} - {\Delta\; t_{43}}}{\Delta\; t_{32}}} - \frac{1}{\tan\;\alpha}} \right)}$

wherein h is a length of R_(x1)-R_(x2) and α is an included anglebetween T_(x1)-T_(x2) and T_(x2)-R_(x2); and

step 5: substituting parameters of Δt₂₁, Δt₃₂, Δt₄₃, l, h and α into thefollowing formula to obtain an estimated value of a moving velocity v ofthe target:

$v = \frac{\sqrt{{h^{2}\Delta\; t_{32}^{2}\sin^{2}\alpha} + \left\lbrack {{l\left( {{\Delta\; t_{21}} - {\Delta\; t_{43}}} \right)} - {h\;\Delta\; t_{32}\cos\;\alpha}} \right\rbrack^{2}}}{\Delta\;{t_{32}\left( {{\Delta\; t_{21}} + {\Delta\; t_{32}} + {\Delta\; t_{43}}} \right)}}$

A method for detection by using the forward acoustic scattering baseddouble-transmitter and double-receiver networking target detectionsystem comprises the following steps of estimating unknown parameters ofd, v and γ when a target successively crosses T_(x1)-R_(x1),T_(x1)-R_(x2), T_(x2)-R_(x1) and T_(x2)-R_(x2) at uniform velocity valong a straight line, with a horizontal distance from a crossing pointof the target on the transmitting-receiving connection lineT_(x1)-R_(x1) to R_(x1) marked as d and an included angle between atarget track and the transmitting-receiving connection lineT_(x1)-R_(x1) marked as γ;

step 1: extracting time of the target crossing transmitting-receivingconnection lines by adopting a direct wave suppression method, whereinsince four transmitting-receiving connection lines exist under adouble-transmitter double-receiver configuration, four time aresuccessively marked as t₁, t₂, t₃ and t₄ according to a time sequence;

step 2: calculating corresponding moving time intervals when the targetcrosses the four transmitting-receiving connection lines as Δt₂₁=t₂−t₁,Δt₃₂=t₃−t₂ and Δt₄₃=t₄−t₃;

step 3: substituting parameters of Δt₂₁, Δt₃₂, Δt₄₃ and l into thefollowing formula to obtain an estimated value of a target distance d:

$d = {{- \frac{\left( {{\Delta\; t_{21}} + {\Delta\; t_{32}}} \right)\left( {{\Delta\; t_{21}} - {\Delta\; t_{32}} - {\Delta\; t_{43}}} \right)}{\Delta\;{t_{32}\left( {{\Delta\; t_{21}} + {\Delta\; t_{32}} + {\Delta\; t_{43}}} \right)}}}l}$

wherein l is a length of T_(x1)-R_(x1);

step 4: substituting parameters of Δt₂₁, Δt₃₂, Δt₄₃, l, h and a into thefollowing formula to obtain an estimated value of an inclined angle α ofa target track:

$\gamma = {\tan^{- 1}\left( \frac{1}{{\frac{l}{h\;\sin\;\alpha}\frac{{\Delta\; t_{43}} - {\Delta\; t_{21}}}{\Delta\; t_{32}}} - \frac{1}{\tan\;\alpha}} \right)}$

wherein h is a length of R_(x1)-R_(x2) and α is an included anglebetween T_(x1)-T_(x2) and T_(x2)-R_(x2); and

step 5: substituting parameters of Δt₂₁, Δt₃₂, Δt₄₃, l, h and α into thefollowing formula to obtain an estimated value of a moving velocity v ofthe target:

$v = {\frac{\sqrt{{h^{2}\Delta\; t_{32}^{2}\sin^{2}\alpha} + \left\lbrack {{l\left( {{\Delta\; t_{43}} - {\Delta\; t_{21}}} \right)} - {h\;\Delta\; t_{32}\cos\;\alpha}} \right\rbrack^{2}}}{\Delta\;{t_{32}\left( {{\Delta\; t_{21}} + {\Delta\; t_{32}} + {\Delta\; t_{43}}} \right)}}.}$

The present invention proposes a forward acoustic scattering baseddouble-transmitter double-receiver networking target detection systemand method thereof. Two transmitting ends and two receiving ends areadopted, anchored at a sea bottom, and arranged in a layout of aparallelogram. Time of a target crossing transmitting-receivingconnection lines are extracted by adopting a proper direct wavesuppression method; and unknown parameters of the horizontal distance,the target velocity and the included angle between the target track andthe transmitting-receiving connection lines are estimated atcorresponding moving time intervals when the target crosses the fourtransmitting-receiving connection lines according to different crossingmodes.

The present invention has the beneficial effects that:

(1) An arrangement mode is simple and flexible, and quick monitoring ofsome important sea areas and sea channels can be realized. Thetransmitting ends and the receiving ends are anchored at the sea bottom,and respective position coordinates can be obtained through GPS. Thus,information of the arrangement form, distance, angle and the like canalso be easily calculated.

(2) Required parameters are only information of moving time of thetarget through a geometrical relationship between a receivingconfiguration and a transmitting configuration. The information of thedistance, the velocity, the inclined angle of the track and the like ofthe target can be simultaneously estimated by combining the informationof the moving time of the target with layout parameters.

(3) After a direct wave suppression method based on adaptiveinterference cancellation is applied, a direct wave is inhibited to anoutput background and a sound field distortion caused by that the targetcrosses the transmitting-receiving connection lines is represented by anoutput peak value. The information of the time of the target crossingthe transmitting-receiving connection lines, extracted by the method,are more accurate and reliable.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of a forward acoustic scattering baseddouble-transmitter double-receiver detection network (parallelogramlayout-crossing case 1);

FIG. 1 shows a schematic diagram of a forward acoustic scattering baseddouble-transmitter double-receiver detection network (parallelogramlayout-crossing case 2);

FIG. 3 shows a schematic diagram of a forward acoustic scattering baseddouble-transmitter double-receiver detection network (rectanglelayout-crossing case 1); and

FIG. 4 shows a schematic diagram of a forward acoustic scattering baseddouble-transmitter double-receiver detection network (rectanglelayout-crossing case 2).

DETAILED DESCRIPTION OF THE INVENTION

The present invention is further described in combination withembodiments and drawings.

A target detection system comprises two transmitting ends and tworeceiving ends; the two transmitting ends and the two receiving ends areanchored at a sea bottom, and formed in a parallelogram layout; the twotransmitting ends are respectively marked as T_(x1) and T_(x2); the tworeceiving ends are respectively marked as R_(x1) and R_(x2);T_(x1)-R_(x1), R_(x1)-R_(x2), R_(x2)-T_(x2) and T_(x2)-T_(x1) form fouredges of the parallelogram; T_(x1)-R_(x2) and T_(x2)-R_(x1) are twodiagonal lines of the parallelogram; a length of T_(x1)-R_(x1) is markedas l; a length of R_(x1)-R_(x2) is marked as h; an included anglebetween T_(x1)-T_(x2) and T_(x2)-R_(x2) is marked as α; formed fourtransmitting-receiving connection lines are: T_(x1)-R_(x1),T_(x1)-R_(x2), T_(x2)-R_(x1) and T_(x2)-R_(x2); and depths of thetransmitting ends and the receiving ends are equal.

Firstly, derivation processes of estimation formulas of a targetdistance d, a moving velocity v and a track angle γ are given.

In FIG. 1, two transmitting ends T_(x1) and T_(x2) are respectivelylocated at A point and B point; and two receiving ends R_(x1) and R_(x2)are respectively located at C point and D point. Positions andconnection lines of the transmitting ends and the receiving ends form aparallelogram, wherein |AC|=1, |CD|=h, and an included angle between ABand BD is marked as α. In this way, four transmitting-receivingconnection lines are formed: AC(T_(x1)-R_(x1)), BC(T_(x1)-R_(x2)),AD(T_(x1)-R_(x2)) and BD (T_(x2)-R_(x2)).

The target successively crosses the four transmitting-receivingconnection lines of AC, BC, AD and BD at a constant velocity v along astraight track, and crossing points of the target and the fourtransmitting-receiving connection lines are marked as E, F, G and H. Ahorizontal distance from the crossing point E of the target on AC to thecrossing point C (R_(x1)) is marked as d, and an included angle betweenthe target track and AC is marked as γ. Vertical lines are respectivelymade to AC from three crossing points F, G and H, and crossed at Ppoint, Q point and R point.

According to a triangle similarity relationship: ΔCFE111□ΔBFH, a formulais obtained

$\begin{matrix}{{{BH}} = {\frac{{\Delta\; t_{32}} + {\Delta\; t_{43}}}{\Delta\; t_{21}}{d.}}} & (1)\end{matrix}$

According to a triangle similarity relationship: ΔAGE□ΔDGH, a formula isobtained

$\begin{matrix}{{{DH}} = {\frac{\Delta\; t_{43}}{{\Delta\; t_{21}} + {\Delta\; t_{32}}}{\left( {l - d} \right).}}} & (2)\end{matrix}$

Since |BH|+|DH|=1, formula (1) and formula (2) are substituted into theformula to obtain

$\begin{matrix}{d = {\frac{\Delta\;{t_{21}\left( {{\Delta\; t_{21}} + {\Delta\; t_{32}} - {\Delta\; t_{43}}} \right)}}{\Delta\;{t_{32}\left( {{\Delta\; t_{21}} + {\Delta\; t_{32}} + {\Delta\; t_{43}}} \right)}}{l.}}} & (3)\end{matrix}$

In a right triangle ΔEHR, |ER|=h sin α/tan γ, and substituted into|ER|+|DH|+h cos α=d to obtain

$\begin{matrix}{\gamma = {{\tan^{- 1}\left( \frac{1}{{\frac{l}{h\;\sin\;\alpha}\frac{{\Delta\; t_{21}} - {\Delta\; t_{43}}}{\Delta\; t_{32}}} - \frac{1}{\tan\;\alpha}} \right)}.}} & (4)\end{matrix}$

In a right triangle ΔEHR,

$\begin{matrix}{{{EH}}^{2} = {{{HR}}^{2}{\left( {1 + \frac{1}{\tan^{2}\gamma}} \right).}}} & (5)\end{matrix}$

Formula (4) is substituted into formula (5) to obtain

$\begin{matrix}{{{EH}} = {\frac{1}{\Delta\; t_{32}}{\sqrt{{\Delta\; t_{32}^{2}h^{2}\sin^{2}\alpha} + \left\lbrack {{l\left( {{\Delta\; t_{21}} - {\Delta\; t_{43}}} \right)} - {h\;\Delta\; t_{32}\cos\;\alpha}} \right\rbrack^{2}}.}}} & (6) \\{{{{Since}\mspace{14mu}{{EH}}} = {v\left( {{\Delta\; t_{21}} + {\Delta\; t_{32}} + {\Delta\; t_{43}}} \right)}},{then}} & \; \\{v = {\frac{\sqrt{{\Delta\; t_{32}^{2}h^{2}\sin^{2}\alpha} + \left\lbrack {{l\left( {{\Delta\; t_{21}} - {\Delta\; t_{43}}} \right)} - {h\;\Delta\; t_{32}\cos\;\alpha}} \right\rbrack^{2}}}{\Delta\;{t_{32}\left( {{\Delta\; t_{21}} + {\Delta\; t_{32}} + {\Delta\; t_{43}}} \right)}}.}} & (7)\end{matrix}$

In FIG. 2, two transmitting ends T_(x1) and T_(x2) are respectivelylocated at A point and B point; and two receiving ends R_(x1) and R_(x2)are respectively located at C point and D point. Positions andconnection lines of the transmitting ends and the receiving ends form aparallelogram, wherein |AC|=1, |CD|=h, and an included angle between ABand BD is marked as a. In this way, four transmitting-receivingconnection lines are formed: AC(T_(x1)-R_(x1)), BC(T_(x1)-R_(x2)),AD(T_(x1)-R_(x2)) and BD (T_(x2)-R_(x2)).

The target successively crosses the four transmitting-receivingconnection lines of AC, AD, BC and BD at a constant velocity v along astraight track, and crossing points of the target and the fourtransmitting-receiving connection lines are marked as E, F, G and H. Ahorizontal distance from the crossing point E of the target on AC to thecrossing point C (R_(x1)) is marked as d, and an included angle betweenthe target track and AC is marked as γ. Vertical lines are respectivelymade to AC from three crossing points F, G and H, and crossed at Ppoint, Q point and R point.

According to a triangle similarity relationship: ΔAFE□ΔDFH, a formula isobtained

$\begin{matrix}{{{DH}} = {\frac{{\Delta\; t_{32}} + {\Delta\; t_{43}}}{\Delta\; t_{21}}{\left( {l - d} \right).}}} & (8)\end{matrix}$

According to a triangle similarity relationship: ΔCGE□ΔBGH, a formula isobtained

$\begin{matrix}{{{BH}} = {\frac{\Delta\; t_{43}}{{\Delta\; t_{21}} + {\Delta\; t_{32}}}{d.}}} & (9)\end{matrix}$

Since |BH|+|DH|=1, formula (8) and formula (9) are substituted into theformula to obtain

$\begin{matrix}{d = {{- \frac{\left( {{\Delta\; t_{21}} + {\Delta\; t_{32}}} \right)\left( {{\Delta\; t_{21}} - {\Delta\; t_{32}} - {\Delta\; t_{43}}} \right)}{\Delta\;{t_{32}\left( {{\Delta\; t_{21}} + {\Delta\; t_{32}} + {\Delta\; t_{43}}} \right)}}}{l.}}} & (10)\end{matrix}$

In a right triangle ΔEHR, |ER|=h sin α/tan(π−γ) and substituted into|BH|−h cos α+|ER|=1−d to obtain

$\begin{matrix}{\gamma = {{\tan^{- 1}\left( \frac{1}{{\frac{{\Delta\; t_{43}} - {\Delta\; t_{21}}}{\Delta\; t_{32}}\frac{l}{h\;\sin\;\alpha}} - \frac{1}{\tan\;\alpha}} \right)}.}} & (11)\end{matrix}$

In a right triangle ΔEHR,

$\begin{matrix}{{{EH}}^{2} = {{{HR}}^{2}{\left( {1 + \frac{1}{\tan^{2}\gamma}} \right).}}} & (12)\end{matrix}$

Formula (11) is substituted into formula (12) to obtain

$\begin{matrix}{{{EH}} = {\frac{1}{\Delta\; t_{32}}{\sqrt{{\Delta\; t_{32}^{2}h^{2}\sin^{2}\alpha} + \left\lbrack {{l\left( {{\Delta\; t_{43}} - {\Delta\; t_{21}}} \right)} - {h\;\Delta\; t_{32}\cos\;\alpha}} \right\rbrack^{2}}.}}} & (13) \\{{{{Since}\mspace{14mu}{{EH}}} = {v\left( {{\Delta\; t\; 21} + {\Delta\; t\; 32} + {\Delta\; t\; 43}} \right)}},{then}} & \; \\{v = {\frac{\sqrt{{\Delta\; t_{32}^{2}h^{2}\sin^{2}\alpha} + \left\lbrack {{l\left( {{\Delta\; t_{43}} - {\Delta\; t_{21}}} \right)} - {h\;\Delta\; t_{32}\cos\;\alpha}} \right\rbrack^{2}}}{\Delta\;{t_{32}\left( {{\Delta\; t_{21}} + {\Delta\; t_{32}} + {\Delta\; t_{43}}} \right)}}.}} & (14)\end{matrix}$

When α=90°, a parallelogram layout shown in FIG. 1 is simplified as arectangle layout shown in FIG. 3. In this case, a calculation formula ofthe target distance d, the inclined angle γ of the track and the movingvelocity v can be simplified as follows:

$\begin{matrix}{{d = {\frac{\Delta\;{t_{21}\left( {{\Delta\; t_{21}} + {\Delta\; t_{32}} - {\Delta\; t_{43}}} \right)}}{\Delta\;{t_{32}\left( {{\Delta\; t_{21}} + {\Delta\; t_{32}} + {\Delta\; t_{43}}} \right)}}l}},} & (15) \\{{\gamma = {\tan^{- 1}\left( {\frac{h}{l}\frac{\Delta\; t_{32}}{{\Delta\; t_{21}} - {\Delta\; t_{43}}}} \right)}},} & (16) \\{v = {\frac{\sqrt{{\Delta\; t_{32}^{2}h^{2}} + {\left( {{\Delta\; t_{21}} - {\Delta\; t_{43}}} \right)^{2}l^{2}}}}{\Delta\;{t_{32}\left( {{\Delta\; t_{21}} + {\Delta\; t_{32}} + {\Delta\; t_{43}}} \right)}}.}} & (17)\end{matrix}$

When α=90°, a parallelogram layout shown in FIG. 2 is simplified as arectangle layout shown in FIG. 4. In this case, a calculation formula ofthe target distance d, the inclined angle γ of the track and the movingvelocity v can be simplified as follows:

$\begin{matrix}{{d = {{- \frac{\left( {{\Delta\; t_{21}} + {\Delta\; t_{32}}} \right)\left( {{\Delta\; t_{21}} - {\Delta\; t_{32}} - {\Delta\; t_{43}}} \right)}{\Delta\;{t_{32}\left( {{\Delta\; t_{21}} + {\Delta\; t_{32}} + {\Delta\; t_{43}}} \right)}}}l}},} & (18) \\{{\gamma = {\tan^{- 1}\left( {\frac{h}{l}\frac{\Delta\; t_{32}}{{\Delta\; t_{43}} - {\Delta\; t_{21}}}} \right)}},} & (19) \\{v = {\frac{\sqrt{{\Delta\; t_{32}^{2}h^{2}} + {\left( {{\Delta\; t_{43}} - {\Delta\; t_{21}}} \right)^{2}l^{2}}}}{\Delta\;{t_{32}\left( {{\Delta\; t_{21}} + {\Delta\; t_{32}} + {\Delta\; t_{43}}} \right)}}.}} & (20)\end{matrix}$

An application example is given in a second part. Firstly, FIG. 1 istaken as an example for description. It is assumed that l=1000 m, h=500m and α=60°. The target successively crosses the transmitting-receivingconnection lines of AC, BC, AD and BD at a velocity v=2.5 m/s along astraight line; a horizontal distance from the crossing point on AC topoint C is d=500 m; and the inclined angle γ of the track is 80°.Relative to a certain reference time (t=0), four crossing time extractedby a direct wave suppression method are respectively t₁=100 s, t₂=166.3s, t₃=230.6 s and t₄=275.9 s. Then, moving time intervals arecalculated: t₂₁=66.3 s, t₃₂=64.3 s and t₄₃=45.3 s. Related parametersare successively substituted into formula (3), formula (4) and formula(7) to obtain the following estimated values: d≈499.7 m, γ≈80.03°, andv≈2.49 m/s.

Taking FIG. 2 as an example, it is assumed that l=1000 m, h=500 m andα=60°. The target successively crosses the transmitting-receivingconnection lines of AC, AD, BC and BD at a velocity v=2.5 m/s along astraight line; a horizontal distance from the crossing point on AC topoint C is d=500 m; and the inclined angle γ of the track is 133°.Relative to a certain reference time (t=0), four crossing time extractedby a direct wave suppression method are respectively t₁=100 s, t₂=202.6s, t₃=240 s and t₄=336.8 s. Then, moving time intervals are calculated:t₂₁=102.6 s, t₃₂=37.4 s and t₄₃=96.8 s. Related parameters aresuccessively substituted into formula (10), formula (11) and formula(14) to obtain the following estimated values: d≈499.3 m, γ ≈133.1° andv≈2.50 m/s.

The direct wave suppression method in the present embodiment adopts thedirect wave suppression method based on adaptive interferencecancellation proposed in patent ZL201418002697.7 to extract the time ofthe target crossing the transmitting-receiving connection lines.

The present invention obtains obvious implementation effects in typicalembodiments. The forward acoustic scattering based double-transmitterdouble-receiver networking target detection method is convenient inoperation, and simple in algorithm, has good robustness, can be used fordetecting underwater targets in important ports, sea channels, straitsand the like, and has wide application prospect.

What is claimed is:
 1. A method for detection by using a forwardacoustic scattering based double-transmitter and double-receivernetworking target detection system, wherein the forward acousticscattering based double-transmitter and double-receiver networkingtarget detection system comprises two transmitting ends and tworeceiving ends anchored at a sea bottom and formed in a parallelogramlayout, the two transmitting ends are respectively marked as T_(x1) andT_(x2); the two receiving ends are respectively marked as R_(x1) andR_(x2); T_(x1)-R_(x1), R_(x1)-R_(x2), R_(x2)-T_(x2) and T_(x2)-T_(x1)form four edges of the parallelogram; T_(x1)-R_(x2) and T_(x2)-R_(x1)are two diagonal lines of the parallelogram; a length of T_(x1)-R_(x1)is marked as l; a length of R_(x1)-R_(x2) is marked as h; an includedangle between T_(x1)-T_(x2) and T_(x2)-R_(x2) is marked as α; and fourtransmitting-receiving connection lines are formed: T_(x1)-R_(x1),T_(x1)-R_(x2), T_(x2)-R_(x1) and T_(x2)-R_(x2); and depths of thetransmitting ends and the receiving ends are equal, the method comprisesfollowing steps of estimating unknown parameters of d, v and γ when atarget successively crosses T_(x1)-R_(x1), T_(x2)-R_(x1), T_(x1)-R_(x2)and T_(x2)-R_(x2) at uniform velocity v along a straight line, with ahorizontal distance from a crossing point of the target on thetransmitting-receiving connection line T_(x1)-R_(x1) to R_(x1) marked asd and an included angle between a target track and thetransmitting-receiving connection line T_(x1)-R_(x1) marked as γ: step1: extracting time of the target crossing transmitting-receivingconnection lines by adopting a direct wave suppression method, whereinsince four transmitting-receiving connection lines exist under adouble-transmitter and double-receiver configuration, four time aresuccessively marked as t₁, t₂, t₃ and t₄ according to a time sequence;step 2: calculating corresponding moving time intervals when the targetcrosses the four transmitting-receiving connection lines as Δt₂₁=t₂−t₁,Δt₃₂=t₃−t₂ and Δt₄₃=t₄−t₃; step 3: substituting parameters of Δt₂₁,Δt₃₂, Δt₄₃ and l into the following formula to obtain an estimated valueof a target distance d:$d = {\frac{\Delta\;{t_{21}\left( {{\Delta\; t_{21}} + {\Delta\; t_{32}} - {\Delta\; t_{43}}} \right)}}{\Delta\;{t_{32}\left( {{\Delta\; t_{32}} + {\Delta\; t_{43}}} \right)}}l}$wherein l is a length of T_(x1)-R_(x1); step 4: substituting parametersof Δt₂₁,Δt₃₂, Δt₄₃, l, h and α into the following formula to obtain anestimated value of an inclined angle α of a target track:$\gamma = {\tan^{- 1}\left( \frac{1}{{\frac{l}{h\;\sin\;\alpha}\frac{{\Delta\; t_{21}} - {\Delta\; t_{43}}}{\Delta\; t_{32}}} - \frac{1}{\tan\;\alpha}} \right)}$wherein h is a length of R_(x1)-R_(x2) and α is an included anglebetween T_(x1)-T_(x2) and T_(x2)-R_(x2); and step 5: substitutingparameters of Δt₂₁,Δt₃₂, Δt₄₃, l, h and α into the following formula toobtain an estimated value of a moving velocity v of the target:$v = {\frac{\sqrt{{h^{2}\Delta\; t_{32}^{2}\sin^{2}\alpha} + \left\lbrack {{l\left( {{\Delta\; t_{21}} - {\Delta\; t_{43}}} \right)} - {h\;\Delta\; t_{32}\cos\;\alpha}} \right\rbrack^{2}}}{\Delta\;{t_{32}\left( {{\Delta\; t_{21}} + {\Delta\; t_{32}} + {\Delta\; t_{43}}} \right)}}.}$2. A method for detection by using a forward acoustic scattering baseddouble-transmitter and double-receiver networking target detectionsystem, wherein the forward acoustic scattering based double-transmitterand double-receiver networking target detection system comprises twotransmitting ends and two receiving ends anchored at a sea bottom andformed in a parallelogram layout, the two transmitting ends arerespectively marked as T_(x1) and T_(x2); the two receiving ends arerespectively marked as R_(x1) and R_(x2); T_(x1)-R_(x1), R_(x1)-R_(x2),R_(x2)-T_(x2) and T_(x2)-T_(x1) form four edges of the parallelogram;T_(x1)-R_(x2) and T_(x2)-R_(x1) are two diagonal lines of theparallelogram; a length of T_(x1)-R_(x1) is marked as e; a length ofR_(x1)-R_(x2) is marked as h; an included angle between T_(x1)-T_(x2)and T_(x2)-R_(x2) is marked as α; and four transmitting-receivingconnection lines are formed: T_(x1)-R_(x1), T_(x1)-R_(x2), T_(x2)-R_(x1)and T_(x2)-R_(x2); and depths of the transmitting ends and the receivingends are equal, wherein the method comprises the following steps ofestimating unknown parameters of d, v and γ when a target successivelycrosses T_(x1)-R_(x1), T_(x1)-R_(x2), T_(x2)-R_(x1) and T_(x2)-R_(x2) atuniform velocity v along a straight line, with a horizontal distancefrom a crossing point of the target on the transmitting-receivingconnection line T_(x1)-R_(x1) to R_(x1) marked as d and an includedangle between a target track and the transmitting-receiving connectionline T_(x1)-R_(x1) marked as γ: step 1: extracting time of the targetcrossing transmitting-receiving connection lines by adopting a directwave suppression method, wherein since four transmitting-receivingconnection lines exist under a double-transmitter double-receiverconfiguration, four time are successively marked as t₁, t₂, t₃ and t₄according to a time sequence; step 2: calculating corresponding movingtime intervals when the target crosses the four transmitting-receivingconnection lines as Δt₂₁=t₂−t₁, Δt₃₂=t₃−t₂ and Δt₄₃=t₄−t₃; step 3:substituting parameters of Δt₂₁, Δt₃₂, Δt₄₃ and l into the followingformula to obtain an estimated value of a target distance d:$d = {{- \frac{\left( {{\Delta\; t_{21}} + {\Delta\; t_{32}}} \right)\left( {{\Delta\; t_{21}} - {\Delta\; t_{32}} - {\Delta\; t_{43}}} \right)}{\Delta\;{t_{32}\left( {{\Delta\; t_{21}} + {\Delta\; t_{32}} + {\Delta\; t_{43}}} \right)}}}l}$wherein l is a length of T_(x1)-R_(x1); step 4: substituting parametersof Δt₂₁, Δt₃₂, Δt₄₃, l, h and α into the following formula to obtain anestimated value of an inclined angle α of a target track:$\gamma = {\tan^{- 1}\left( \frac{1}{{\frac{l}{h\;\sin\;\alpha}\frac{{\Delta\; t_{43}} - {\Delta\; t_{21}}}{\Delta\; t_{32}}} - \frac{1}{\tan\;\alpha}} \right)}$wherein h is a length of R_(x1)-R_(x2) and α is an included anglebetween T_(x1)-T_(x2) and T_(x2)-R_(x2); and step 5: substitutingparameters of Δt₂₁, Δt₃₂, Δt₄₃, l, h and α into the following formula toobtain an estimated value of a moving velocity v of the target:$v = {\frac{\sqrt{{h^{2}\Delta\; t_{32}^{2}\sin^{2}\alpha} + \left\lbrack {{l\left( {{\Delta\; t_{43}} - {\Delta\; t_{21}}} \right)} - {h\;\Delta\; t_{32}\cos\;\alpha}} \right\rbrack^{2}}}{\Delta\;{t_{32}\left( {{\Delta\; t_{21}} + {\Delta\; t_{32}} + {\Delta\; t_{43}}} \right)}}.}$